1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a method and an apparatus for driving a liquid crystal display device that adjust brightness of light generated by a back light device to improve a contrast ratio of a moving image.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device controls light transmittance of liquid crystal cells in accordance with data signals applied thereto, to thereby display an image. In particular, an active matrix type LCD device includes a switching device for each cell and has various applications, such as a monitor for a computer, office equipment, and a cellular phone, because of their high quality image, lightness, thin thickness, compact size, and low power consumption. A thin film transistor (TFT) is generally employed as the switching device for the active matrix type LCD device.
FIG. 1 is a schematic block diagram illustrating a driving apparatus for a liquid crystal display device according to the related art. In FIG. 1, an LCD driving apparatus includes a liquid crystal display panel 2 having m×n liquid crystal cells Clc arranged in a matrix-like manner at intersections between data lines D1 . . . Dm and gate lines G1 . . . Gn, a data driver 4 for applying data signals to the data lines D1 . . . Dm, a gate driver 6 for applying gate signals to the gate lines G1 . . . Gn and a dummy gate line G0, and a gamma voltage supplier 8 for supplying gamma voltages to the data driver 4, and a timing controller 10 for controlling the data driver 4 and the gate driver 6 using signals applied from a system 20.
In addition, each of the liquid crystal cells Clc includes a thin film transistor TFT. The thin film transistor TFT applies a data signal from a respective one of the data lines D1 . . . Dm to the liquid crystal cell Clc in response to a scanning signal from a respective one of the gate lines G1 . . . Gn. Each of the liquid crystal cells Clc also includes a storage capacitor Cst. The storage capacitor Cst maintains a voltage of the liquid crystal cell Clc.
Further, the data driver 4 converts digital video data R, G and B into analog gamma voltages, i.e., data signals, corresponding to gray level values in response to a control signal CS from the timing controller 10, and applies the analog gamma voltages to the data lines D1 . . . Dm. The gate driver 6 sequentially applies a scanning pulse to the gate lines G1 . . . Gn in response to the control signal CS from the timing controller 10, to thereby select horizontal lines of the liquid crystal display panel 2 to be supplied with the data signals.
The system 20 applies vertical/horizontal synchronizing signals Vsync and Hsync, a clock signal DCLK and a data enable signal DE to the timing controller 10. Further, the system 20 controls a power supply 12. In particular, the LCD driving apparatus includes a DC/DC converter 14 for boosting or dropping a voltage of 3.3V inputted from the power supply 12. Thus, the DC/DC converter 14 generates a gamma reference voltage, a gate high voltage VGH, a gate low voltage VGL and a common voltage Vcom (not shown).
Moreover, the timing controller 10 generates the control signal CS for the data driver 4 and the gate driver 6 using the vertical/horizontal synchronizing signals Vsync and Hsync, the clock signal DCLK and the data enable signal DE inputted from the system 20. Although not shown, the control signal CS for the gate driver 6 includes a gate start pulse GSP, a gate shift clock GSC and a gate output enable signal GOE, and the control signal CS for the data driver 4 includes a source start pulse SSP, a source shift clock SSC, a source output enable signal SOE and a polarity control signal POL. The timing controller 10 also re-aligns the video data R, G and B from the system 20 before applying them to the data driver 4.
Furthermore, the LCD driving apparatus includes an inverter 16 for driving a back light 18. The inverter 16 applies a driving voltage or a driving current for driving the back light 18. The back light 18 generates light corresponding to the driving voltage or the driving current from the inverter 16 for the liquid crystal display panel 2.
In order to display a vivid image on the liquid crystal display panel 2, a distinct contrast between brightness and darkness must be made in correspondence with a data. However, since the back light 18 according to the related art produces the same degree of brightness irrespectively of a data, it was difficult to display a dynamic and fresh image.